The overall goals of this longitudinal study are to examine the etiologic determinants of adolescent drug use and the consequences of use on the individual's functioning. The original sample consisted of 976 youngsters and their mothers who were first seen when the children were ages 1-10 (T1), then at 9-18 (T2), and again at 11-20 (T3). A fourth data collection (T4) is proposed to accomplish the following: (1) to examine interrelations and interactions of personality, family, peer, and ecological factors (starting in early childhood) as they affect the course of drug use over time (i.e., onset, stability, and change); (2) to study the consequences of long-term marijuana (and other illicit drug) use on adolescent intra- and interpersonal functioning; (3) to initiate a three generation study in which the offspring of the original sample child will be assessed using observational data (at about age 2) to see how earlier generational factors lead to the development of childhood precursors of later drug use. Also to be examined, using data on the original study child and his/her parents and siblings, is the familial transmission of drug and alcohol use behavior. As with the previous data collections, separate interviews with mother and child will be conducted in their own homes by trained interviewers. Scales with adequate psychometric properties measuring the independent variables will be developed from the interview schedules. The primary analytic technique will be either hierarchical regression or causal analysis. The significance of this study lies in its longitudinal design with in-depth intra- and interpersonal data available at several crucial stages of development. These data allow us not only to examine the pathways to drug use from the very beginning but also to study the course of drug behavior over time, i.e., the factors related to the youngster's becoming more (or less) involved in drug use over a span of years. Such knowledge will help pinpoint those youngsters at risk for increased drug involvement and will provide detailed and specific guidelines for prevention and treatment. Our longitudinal study of the consequences of drug use is unique in that the long-term effects of use can be evaluated to see if their impact is cumulative. In addition, identification of childhood and early adolescent factors that can mitigate or compensate for the impact of drug consequences on later functioning would provide additional aids for effective prevention and treatment efforts.